The values of the second dissociation constant, pK 2 , and related thermodynamic quantities of 3-[(1,1-dimethyl-2-hydroxymethyl)amino]-2-hydroxypropanesulfonic acid (AMPSO) have already been reported in previous investigations at 12 temperatures over the temperature range (278.15 to 328.15) K, including 310.15 K (J. Solution Chem. 1997, 26, 309-317). This paper reports the results for the pH of nine buffer solutions free of the chloride ion with compositions: (a) AMPSO (0.04 mol+ NaAMPSO (0.02 mol • kg -1 ); (f) AMPSO (0.06 mol • kg -1 ) + NaAMPSO (0.03 mol • kg -1 ); (g) AMPSO (0.08 mol • kg -1 ) + NaAMPSO (0.01 mol • kg -1 ); (h) AMPSO (0.08 mol • kg -1 ) + NaAMPSO (0.02 mol • kg -1 ); and (i) AMPSO (0.08 mol • kg -1 ) + NaAMPSO (0.08 mol • kg -1 ). The remaining 13 buffer solutions (j to v) have saline media of the ionic strength I ) 0.16 mol • kg -1 , matching closely to that of the physiological sample. Conventional pa H values, designated as pH(s), for all nine buffer solutions (a to i) without the chloride ion and thirteen buffer solutions with the chloride ion (j to v) at I ) 0.16 mol • kg -1 from (278.15 to 328.15) K have been calculated. The operational pH values for six buffer solutions at (298.15 and 310.15) K have been determined based on the difference in the values of the liquid junction potentials between the blood phosphate standard and the experimental buffer solutions. Five of these buffers are recommended as standards for the physiological pH range 7.5 to 8.5.

The values of the second dissociation constant, pK 2 of N-(2-hydroxyethyl) piperazine-N'-2-ethanesulfonic acid (HEPES) have been reported at 12 temperatures over the temperature range 5 to 55°C, including 37°C. This paper reports the results for the pa H of eight isotonic saline buffer solutions with an I = 0.

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The values of the second dissociation constant pK 2 and related thermodynamic quantities of the ampholyte 3-(N-morpholino)-2-hydroxypropanesulfonic acid (MOPSO) have been previously determined at temperatures from (278.15 to 328.15) K. In this study, the pH values of two buffer solutions without NaCl and three buffer solutions with NaCl having ionic strengths (I = 0.16 mol·kg −1 ) similar to those in blood plasma, have been evaluated at 12 temperatures from (278.15 to 328.15) K using an extended form of the Debye-Hückel equation, since the Bates-Guggenheim convention is valid up to I = 0.1 mol·kg −1 . The liquid junction potentials (E j ) between the buffer solutions of MOPSO and saturated KCl solution of the calomel electrode at (298.15 and 310.15) K have been estimated by measurement with a flowing junction cell. These values of E j have been used to ascertain the operational pH values at (298.15 and 310.15) K. Three buffer solutions of MOPSO are recommended as useful reference solutions for pH measurements in saline media of ionic strength I = 0.16 mol·kg −1 .

The values of the second dissociation constant, pK 2 , and related thermodynamic quantities of 3-[N,Nbis (2-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO) have already been reported over the temperature range 5 to 55°C including 37°C. This paper reports the pH values of four NaClfree buffer solutions and four buffer composition containing NaCl salt at I = 0.16 mol·kg −1 . Conventional pa H values are reported for all eight buffer solutions. The operational pH values have been calculated for four buffer solutions recommended as pH standards, at 25 and 37°C after correcting the liquid junction potentials with the flowing junction cell.